1. Field of the Invention
The present invention relates generally to circuits generating reference voltages, and more specifically to techniques for maintaining a reference voltage constant against load variations.
2. Related Art
Devices/systems often require a reference voltage to be supplied for operation. For example, an analog to digital converter often compares a strength (e.g., voltage) of an input signal with a fixed voltage to generate a corresponding digital code representing the strength of the input signal. Such fixed voltages supplied from a voltage source to external components are referred to as reference voltages.
One or more corresponding circuit portions of a device/system receiving a reference voltage act as a load (impedance) to a voltage source providing the reference voltage, and may draw current from the source. For example, in a pipeline ADC using switched capacitor circuits internally, capacitor banks act as a load to a voltage source providing the reference voltage.
The load impedance presented to a voltage source often changes with time. As a result, at least at time points when the load changes, the strength of the reference voltage may deviate from the desired reference level, often exhibiting overshoot/undershoot, ringing, DC offset (droop), etc., which may be undesirable.
Several aspects of the present invention provide a reference voltage which is maintained constant against such load variations.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.